1. Field of the Invention
The present invention relates to a touch response apparatus for an electronic musical instrument. More particularly, it relates to a touch response apparatus for an electronic keyboard instrument wherein capacitors and resistors are used as a key touch detector circuit, a touch response function is effected by such key touch detector circuits smaller in number than keys, and the difference in touch response which is created by the difference between the mounting positions of the contacts of a black key and a white key is compensated.
2. Description of the Prior Art
In conventional electronic musical instruments, in order to effectively express the initial control of a musical sound by a key operation, it is common practice to control the performance sound upon detecting a key depression speed at the key operation.
In an apparatus furnished with such touch response function in which the volume, the tone color etc. of a musical sound to be generated are controlled by detecting the key depression speed, a plurality of key depression speed detecting means are required for controlling the volume and tone color of the musical sound to-be-generated in correspondence with the key depression speed besides an ordinary key-on signal.
Various functions for producing such key depression speed detecting signal have been proposed.
FIG. 1 is a sketch diagram of a key portion for explaining a prior-art key depression detecting means. Referring to the figure, a white key WK and a black key BK are respectively cantilevered at supporting points X.sub.1 and X.sub.2. When contacts RC.sub.1, RC.sub.2 or RC.sub.3, RC.sub.4 of conductive rubber or the like which are mounted on the lower surface of the white key or black key and which have lengths unequal to each other are depressed, the contact pieces of switches SW.sub.1, SW.sub.2 or SW.sub.3, SW.sub.4 fall into "on" states. Thus, key depression speed detecting means DET detects the speed signal of the white or black key corresponding to the speed of depression in the direction of arrow A or B, by using the time period from the closing of the switches SW.sub.1 or SW.sub.3 to the closing of the switches SW.sub.2 or SW.sub.4, respectively.
More specifically, when the white key WK is depressed in the direction A, it turns counterclockwise about the fulcrum X.sub.1. Therefore, the contact RC.sub.1 first comes into contact with the switch SW.sub.1, and the contact RC.sub.2 comes into contact with the switch SW.sub.2 somewhat later. Likewise, when the black key BK is depressed in the direction B, the contact RC.sub.3 comes into contact with the switch SW.sub.3, whereupon the contact RC.sub.4 comes into contact with the switch SW.sub.4. A key depression speed can accordingly be obtained by measuring the period of time between the preceding contact and the succeeding contact, for example by using the charging or discharging amounts of capacitors provided in the key depression speed detecting means DET.
As a first key depression detecting means in the prior art, the key depression speed detecting means DET is disposed for each key. It includes a capacitor and a resistor. The key depression speed detection signal is detected as the amount of the charge of the capacitor by the aforementioned switches corresponding to the respective keys on the basis of the charging to the capacitor or the discharging to the resistor.
With such arrangement, the key depression speed detecting means DET must be disposed for each key, resulting in the disadvantage that the number of constituent parts increases.
Known as a second key depression detecting means is a digital arrangement wherein the period of time from the starting of key depression to the end thereof, that is, the period of time from the turn-on of the first or third switch SW.sub.1 or SW.sub.3 to the turn-on of the second or fourth switch SW.sub.2 or SW.sub.4 in the case of FIG. 1, is counted by a counter circuit or the like, and the count data is used as the key depression speed detection signal. Also this measure has the disadvantage that the counter circuits must be disposed for the respective keys. Another disadvantage is that the conversion of input data is necessary or that the external control is difficult.
Furthermore, according to the setup shown in FIG. 1, both the white and black keys must be provided with the contacts RC.sub.1, RC.sub.3 and the contacts RC.sub.2, RC.sub.4 at equal distance l.sub.1 and l.sub.2 from the fulcra X.sub.1, X.sub.2. It is extremely difficult and complicated to dispose such contacts RC.sub.1 and RC.sub.3, or RC.sub.2 and RC.sub.4 at the positions of the equal distances for a plurality of white and black keys. As another disadvantage, the touch response state of the black key or the structure of the keys becomes very unnatural.